Liquid development of electrostatic images with carbon black and a solid organic pigment



United States Patent 3,391,015 LIQUID DEVELOPMENT OF ELECTROSTATIC IMAGES WITH CARBON BLACK AND A SOLID ORGANIC PIGMENT Donald L. Fauser, Cleveland, Ohio, assignor to Harris- Irgtgrtype Corporation, Cleveland, Ohio, a corporation 0 hi0 No Drawing. Filed Apr. 27, 1964, Ser. No. 362,986 1 Claim. (Cl. 117-37) ABSTRACT OF THE DISCLOSURE A stable self-fixing liquid developer includes carbon 'black as the primary color ingredient, and a solid organic pigment insoluble in the carrier liquid, and which functions as a surface active agent. A liquid resin is used as the fixing agent, and the pH of the carbon black and that of the organic pigment are essentially close to each other to provide marking particles (carbon black and organic pigment) which have essentially the same electrophoretic mobility. Above pH 6.4 the developer polarity is positive while below pH 6.4 the polarity is negative. Various resins, carbon blacks, organic pigments, and carrier liquids are described as well as formulating procedures and methods of developing.

This invention relates to electrostatic printing and more particularly to an improved liquid developer including carbon black, the method of making such a developer and the method of using such a developer to develop an electrostatic latent image.

Recently, developer systems have been proposed which make it possible to develop images with improved clarity, contrast and definition. One such system is disclosed in the Metcalfe et al. article on Liquid Developers for Xerography, the Journal of Scientific Instrument, vol. 32, February 1955, pp. 74 and 75. The developer disclosed in this article represents a relatively simple system including a dispersion of finely divided carbon black in an electrically insulating liquid. Such a developer may be employed with photoconductive plates, drums or papers, and it may be necessary to employ a separate fixing operation in order to achieve the desired permanency of the developed image.

The use of carbon blacks as a developer pigment provides the advantages of good coverage and opacity by a relatively inexpensive pigment which is chemically stable and of small particle size. Additional-1y, most reproduction systems are based on a black on white copy of an original document or reproduction of a transparency. Finely divided carbon blacks however are somewhat difficult to formulate into a stable liquid developer because of their strong tendency to fiocculate, agglomerate or settle out of the liquid suspending medium.

As a general rule, finely divided carbon blacks are porous or structured in nature and exhibit a non-ionic chemical nature, are generally electrically conductive and include contaminants such as absorbed gases, non-volatile residues and absorbed water. The characteristics of the carbon blacks vary widely from one type to another depending on the method of preparation; for example, the characteristics of channel blacks may differ from bone blacks, acetylene blacks or lampblacks. Additionally, with any particular type of carbon black, the characteristics thereof may vary from one batch to the next as a result of variations in the nature of the starting material used in the process of forming the finely divided particles.

The above difiiculties become quite noticeable when carbon black pigments are compounded to render them 3,391,015 Patented July 2, 1968 self-fixing in a liquid developer system as by the use of a resin envelope which causes adhesion of the deposited pigment to the surface.

Accordingly, it is a primary object of the present invention to provide a self-fixing liquid developer for developing an electrostatic latent image wherein the primary color pigment is carbon black.

Another object of the present invention is the provision of a two-phase liquid developer composition including marking particles dispersed in an electrically insulating liquid wherein the marking particles includes a carbon black pigment and a liquid resin, and wherein a solid surface active agent is associated with the carbon black and cooperates with the resin and the carbon black to form the dispersed phase.

Another object of the present invention is the provision of a relatively stable liquid developer which is selffixing in nature and wherein the primary color pigment is a carbon black pigment which is stabilized by use of an organic pigment which functions as a solid surface active agent.

A further object of the present invention is to provide a stable self-fixing liquid developer for electrostatic photography wherein the primary color ingredient is carbon black pigment, and wherein the pH of the carbon black pigment as determined in an aqueous medium is coordinated and correlated with the pH, as similarly determined, and color of a solid surface active agent to provide developers of the proper polarity, stability, and hue and capable when deposited of providing the proper image density.

A further object of the present invention is to provide an improved method of formulating a stable carbon black liquid developer for electrostatic photography.

A further object of the present invention is to provide an improved method of developing an electrostatic latent image with a self-fixing liquid developer wherein the primary pigment is a carbon black.

The liquid developer of the present invention includes a marking particle which is dispersed in an electrically insulating liquid, and the marking particle includes a carbon black pigment, or aggregate or mixture of carbon black pigments as the primary color agent and a solid surface active agent associated therewith, both the surface active agent and the carbon black pigment being surrounded by an encapsulating liquid resin envelope. The developer is a two-phase system including a carrier liquid which is an electrically insulating liquid and a colloidally dispersed or emulsified phase which is the marking particle.

The electrically insulating liquid is preferably a nonpolar liquid having a volume resistivity sutficiently high to prevent discharge of the electrostatic latent image, for example to about 10 ohm/centimeters or higher. The liquid is characterized by a Kauri-Butanol value, or solvency power, sufficiently low to permit formation of two phases in the presence of the resin in accordance with the present invention, but not so low as to collapse the gelatinous resin envelope thereby destroying the stability of the emulsion or dispersion and not so high as to dissolve the resin envelope.

Liquid parafiins, straight or branched chain, synthetic or distilled from petroleum and of low K-B value have provided good results as carrier liquids. These materials promote developer stability in that they absorb a minimum amount of atmospheric water vapor while exhibiting a rapid evaporation rate which is a function primarily of the molecular weight so that the liquid may be removed within a relatively short period of time. If changes in K-B value are indicated, it may be adjusted upward by adding as needed, a relatively small quantity of liquid having a relatively high K-B value, for example aromatics, olefins, ketones, esters and the like to provide a carrier having a K-B value in the range of about or to 70.

It is preferred in accordance with the present invention that the carrier liquid be an odorless high molecular weight liquid paralfin which is relatively free of nonvolatile residues which would tend to contaminate the coating of the image bearing surface. Such contamination is detrimental to image quality particularly in those instances in which a series of images are to be developed seriatim on the same image bearing surface. This type of liquid carrier is characterized by a clear, water white color, absence of sulfin compounds and olefins and generally having a boiling point in the range of 200 to 400 F.

Typical examples of other liquid materials which may be utilized include halogenated hydrocarbons ranging in molecular weight from about 137 to 205 and having a K-B value ranging from about 25 to 70. Other materials which may be utilized include n-pentane, n-hexane, nheptane, V.M. & P. naphtha, high-flash V.M. & P. naphtha, naphthanol mineral spirits, mineral spirits No. 10, Stoddard solvent, Varsol-l, Varsol-Z, high-flash mineral spirits, odorless mineral spirits, and kerosene, which eX- hibit a K-B value in the range of 25 to about 40. Additional materials such as Isopar G and Isopar H, which are believed to be synthetic isoparaflins, and available from the Humble Oil and Refining Company in different boiling point ranges but essentially similar in K-B values may also be utilized.

The carbon black pigment in accordance with the present invention may be an acetylene black, a lampblack, a gas furnace black, an oil black, a channel black or a bone black or mixtures thereof. Each of these carbon black materials exhibits common properties such as electrical conductivity, included or occluded contaminants including gases, non-volatile residues or ash and absorbed water. The particle sizes of the pigment vary from 7 to 26 millimicrons in the case of channel or impingement blacks while the furnace blacks range in particle diameter from fixing carbon black developers wherein a liquid resin is associated with the carbon black to provide the dispersed phase and to effect fixing of the pigment upon simultaneous deposition of the carbon black and resin.

The carbon blacks which have been used in accordance with the present invention are the following:

Type and designation: pH Acetylene black, compressed 7.8 Larnpblack, Superjet M-l011 8.83 Gas furnace-Witcoblak Fl 9.78 Gas furnaceContinex SRF 9.71 Gas furnaceMolacco 9 Gas furnaceStatex B12 10.41 Gas furnace-Neotex 7.83 Oil furnace-SPF 7.93 Oil furnaceContinex ISAF 8.22 Oil furnace-Witcoblak F-3 8.18 Oil furnace-Continex FEF 8.04 Oil furnaceContinex HAF 7.78 ChannclWitcoblak 100 5.58 ChannelContinental A 5.38 Channel-Continental AA 4.75 ChannelRaven 11 5.77 Channel-Royal Spectra 3.81 ChannelNeo Spectra Mark III 3.68

In order to provide the characteristics which facilitate formation of a stable dispersion of carbon black, it has been discovered in accordance with the present invention that the association of the carbon black with a solid surface active agent permits formulation of a two-phase developer system wherein one phase comprises the carbon black pigment and the surface active agent surrounded by a liquid resin envelope and the other phase comprises the carrier liquid. In accordance with the present invention, the solid surface active agent is preferably an organic pigment having a relatively low specific gravity. Typical of the pigments preferred in accordance with the present invention are as follows:

Pigment Supplier pH Monastral Violet R RT-791-D El. duPont deNemours & Co 9. 29 Monastral Red B RT790D d0 8. 78 Permanent Red-2B, Citation, Lt. (Ba) 1058 9.84 Permanent Red-2B, Citation, Med. Yel. 10 8. 32 Permanent Red-2B, Citation, Toner 1053.. 8.52 Permanent Carmine Toner 1D-8710 6 45 Pyrazell Red Toner (pyrazolone) 1D-l970 Bontone Brown Y 7D-2250 Yellow Toner 3D-1S40 Benzidine Yellow Toner 3D-2052 Benzidine Transfast Yellow 1275 Sunset Gold Toner 3D8820 Green Gold, YT-562D Monastral Green B GT-G Pigment Green B 3890 Permanent Green 300 3D8322 Phthalocyanine-Zulu Green, 3826 Phospho-Tungstate Bluegrass Green 3910. Monastral Blue BF BT-425-D PhthalocyanineZulu Blue 4860 Phthalocyanine-Zulu Blue, Flee. resist 4863 Black N o. 1 2082 27 to 78 millimicrons. Acetylene blacks on the other hand exhibit a particle configuration which is chain-like in structure and somewhat larger than the particle diameters of the channel or furnace blacks. The bone blacks are typical of the high ash content carbon blacks.

It has been noted that carbon blacks, such as the furnace blacks possess a high ash content and exhibit an alkaline pH while channel blacks on the other hand, which possess a low ash content, exhibit an acid pH. The experimental pH values appear to correspond with the ash content to the extent that as the ash content increases the pH increases.

The chemical nature, electrical and structural makeup as well as high oil absorption characteristics of the carbon blacks constitute properties which tend to interfere with formation of stable two-phase developers. As a result, some difiiculty has been encountered in preparing self- Phthalocyanine-Crontoniast Blue {SD-4350 N CNF Toner Black Pigment No. 90, Master Standard s m ws rn ps ew e p=p b woomwmmowwoooowenw v si iwoomomqmwwwuoomw The resins usable to form the dispersed phase in accordance with the present invention are preferably liquid and are characterized by a decreasing solubility with increasing concentration of carrier liquid of the type previously described, and their ability to provide an organosol,

' emulsion or stable suspension of non-fiocculating colloidal particles when in the presence of a carrier liquid. The resin is compatible with the carrier liquid up to a predetermined relative proportion of carrier liquid to resin wherein the viscosity of the mixture is relatively high as compared to the viscosity of the carrier. Above the predetermined relative proportion of carrier liquid to resin, the resin and carrier liquid are not compatible and form a stable two-phase system including dispersed particles of resin rather than a sedimentary precipitate, and the viscosity of the two-phase stable dispersion of resin in carrier is essentially the viscosity of the carrier. These resins are characterized by their ability to form a particulate colloidal dispersion, stable emulsion, organosol or suspension when diluted to between 4 and 800 times their weight with a carrier liquid having a K-B value of between about and 70.

The resin is preferably a viscous liquid at a temperature less than 150 C. but may be a solid and dissolved in a relatively small amount of solvent to provide a liquid resin mixture. A suitable solvent may be for example a non-polar solvent or thinner of relatively low K-B value, and the resin and solvent are so coordinated and correlated that the solvent will not subsequently function as a contaminant and the combined characteristics of the resin and solvent are such that they are capable of forming an organosol when diluted with a carrier liquid of the above type to a concentration wherein a substantial fraction of the resin is incompletely soluble as a molecular dispersion in the carrier liquid. The resins which may be used in accordance with the present invention are preferably alkyd resins, or condensation or esterification products of one or more saturated or unsaturated polycarboxylic acids and one or more polyhydric alcohols. Such resins may be modified with one or more mono carboxylic acids such as drying or nondrying vegetable oil acids, and their solubility may be influenced by the extent of condensation, which controls the average molecular weight and the molecular weight distribution of the alkyd polymer. These particular materialsappea-r advantageous because they produce clear, hard, fast drying films resistant to aqueous solutions and hydrocarbon solvents. The latter characteristic is of significance particularly wherein an image bearing member having a developed image thereon is to be treated to form :a second image.

The ability of the alkyds to dry in air depends upon the oil length of the alkyd and the nature of the oil modification thereof. Drying oils containing unsaturated linkages combine with oxygen from the atmosphere to form a reaction product that polymerizes the modifying oils to form a continuous carrier liquid insoluble film. According-1y, one feature of the present invention is the fact that the resin component may be caused to fix to an imaging surface by removing the surrounding carrier liquid thereby providing access to atmosphere oxygen for polymerization as previously noted. Generally, alkyd resins tare classified according to the relative amount of oil used with respect to the phthalic anhydride, and the short oil alkyds generally contain to 45% oil, the medium oil alkyds 45 to 65% oil and the long oil alkyds between 65 and 85% oil.

As the oil length decreases, acid value, viscosity, molecular complexity and cross-linking increase while solubility in high boiling petroleum and aliphatic solvents decrease. In accordance with the present invention the alkyd resins are preferred since they appear to be superior in maintaining charge polarity while providing hard and scuff resistant films.

Alkyds which may be used for example include resins made up of 60 to 70 parts mixed linoleic and linolenic fatty acids and about to parts of approximately equivalent molecular proportions of pentaerythritol and phthalic anhydride. Also, alkyd-s of about 55 to 65% mixed linseed oil fatty acids reacted with glycerol and phthalic anhydride in molecular ratios of 1.05 to 1.15 molecules of glycerol per molecule of phthalic anhydride are useful.

An alkyd prepared so as to be a hydrocarbon soluble resin of acid value of less than 15 and viscosity less than B 'at 40% non-volatile content wherein the viscosity is rated in the Gardner-Holdt scale at 77 F. has also been found to be satisfactory.

In addition, oleo resin varnish vehicle comprised of rosin modified phenolic resin and mixed linseed and tung oil in such proportions as to provide 70 to 80 gallens of mixed oil per gallons of oleo resin varnish operates satisfactorily. This particular material is heat blended and bodied at a temperature in excess of 525 -F. until the resin modified oil has a viscosity greater than A but less than C at 40% non-volatile content in mineral spirits having a K-B value equal to 35, the viscosity having been measured on a Gardner-Holdt scale at 77 F.

The alkyds which have been successfully used were modified with linseed oil, castor oil, soya oil, dehydroxylated' castor oil, coconut oil, cotton seed oil, otiticia, palmitic oil, peanut oil, safflower, tall oil or mixtures thereof. These alkyds may be modified to provide the desired oil content and other properties as heretofore noted.

The alkyd to be used may be a long, medium or short oil alkyd wherein the proportion of oil is coordinated and correlated with the K-B value of the carrier liquid to provide a resin which is capable of forming an organosol at a dilution level wherein the resin becomes substantially insoluble in the carrier liquid. In addition, fractions of such alkyds may exhibit an intrinsic viscosity as measured in substantially anhydrous ketone solvents which varies between 1.0 and 0.01 indicating a molecular weight range between 2,000 and as high as 100,000. These resins are also characterized by an acid value between 3 and 50, and it is preferred that the acid value be between about 3 and 10.

In addition to the resins previously mentioned, oleo resinous vinyl polymers and copolymers, and modifications thereof may be utilized. For example, the reaction product of the vinyl alcohol and long chain fatty acids or mixtures thereof such as myristic, palmitic, oleic, stearic, behenic and ricinoleic acids and the like is prepared by condensation and thereafter polymerized through the double bonds of the vinyl or ethylenically unsaturated portion of the resultant reaction product previously associated with the vinyl alcohol.

In formulating the developer in accordance with the present invention, the first step includes dispersing a predetermined amount of carbon black and solid surface active agent in enough liquid resin or binder to exceed the oil absorption end point of the mixture. The amount of binder to be used may be determined by titrating the combined pigment with binder and blending the two together until sufficient binder has been added to wet out the pigment completely, and the predetermined amount of binder may vary with each different type carbon black, or solid surface active agent, or mixtures thereof. The mixture of the binder and combined pigments may be processed on a ball mill or three roll mill or other conventional pigment grinding equipment. The viscosity may be adjusted by the addition of carrier liquid to provide a mixture having a consistency suitable for processing in accordance with the particular apparatus being employed. At this point, other additives may be incorporated into the mixture to improve pigment dispersion or promote organosol formation or to facilitate the chemical reaction by which the binder becomes fixed to the surface upon which it is deposited. For example, dryers such as the metal salts of fatty acids and the like may be added in small percentages.

The ratio of combined carbon black and solid surface active agent pigment to binder solids by weight at the oil absorption end point is approximately 1 to 2.5. This ratio and ratios as small as 1 to 70 may be utilized in the developers of the present invention with the preferred ratio being about 1:14 to 1:20.

In cases where the resin is present in large amounts in proportion to the pigment, the optical density of the image due to pigment deposition is somewhat less than that desired, while with too little resin, an envelope may not be formed, or the developed image may exhibit less smudge resistance and poor squeegee characteristics, and the developer may exhibit a tendency to fiocculate or settle out and agglomerate.

After the grinding operation the resultant material is a paste having 55% to 60% solids content with the continuous homogeneous phase or solution including the binder and carrier containing the dispersed combination of pigments. In this form, the binder acts as a solvent for the carrier, and the viscosity of the liquid resin binder carrier solution is relatively high and is characteristic of the viscosity of the binder itself.

The toner paste is thereafter reduced in solids content to approximately 25% by the addition of aliquots of carrier liquid until the phase inversion takes place at which point the carrier becomes the continuous phase and the resin becomes the dispersed phase resulting in the two-phase organosol or emulsion type system in which the combination of pigment and solid surface active agent is entrained or carried by the dispersed phase. At this point, the toner concentrate has a relatively low viscosity which is essentially the viscosity of the carrier. Although the percentage .of solid materials in the concentrate is somewhat higher than that customarily used during development, each portion of the dispersed phase or each dispersed marking particle carries a characteristic charge which is primarily a function of the pH of the surface active agent as determined from pH measurements taken in deionized or distilled water.

To provide a composition suitable for development of an electrostatic latent image, the toner concentrate is reduced in solids content (pigment, surfactant and resin) to between .25% and 3% either by adding the concentrate to the carrier or by adding the carrier to the concentrate. Since the organosol was previously formed in the toner concentrate, the addition of further carrier operates only to reduce the solids content per unit volume, or percentage of marking particles.

Useful toner concentrates have a dilution number of about 4 to 6 while the developer has a dilution number of about 20 to 800, the dilution number being defined as the weight of carrier divided by the weight of binder.

It is preferred in accordance with the present invention that the surface active agent be solid as opposed to liquid in order to maintain the surface active agent in close association with the carbon black pigment and prevent its dispersion through the bulk of the carrier liquid. Liquid surface active agents, as generally understood, are molecules composed of two separate portions one of which is generally sufiiciently compatible with the solvent to bring the entire molecule into solution. The other portion of the molecule generally is incompatible with the solvent so that the molecules tend to concentrate at an interface. Of the oil soluble surface active agents, which are generally long chain hydrocarbons and ionic in nature, the polar groups are rejected by the carbon black surface which is non-ionic in nature. Even though the liquid surface active agents may be absorbed into the pores of the carbon black pigment, the ability to function as a surface active agent as required for emulsion formation in accordance with the present invention is impeded by the failure of the molecule to orient itself properly, that is with the polar or non-polar group in association with the pigment and the other group extended into the binder. In the case of liquid non-ionic surface active agents which rely on hydrogen bonding for their orientation or pigment wetting capability, the low degree of hydrogen bonding of the carbon blacks tends to reduce their efficiency as surface active agents for the purposes of the present invention.

Both non-ionic and ionic liquid surface active agents exhibit solubility in the carrier liquids used in the present invention, and the dispersion or solution .of either or both of these type surface active agents operates to increase the conductivity of the carbon black as well as the conductivity of the carrier liquid.

The organic pigments previously noted perform the function of a surface active agent when used in combination with a resin and a carbon black pigment, al-

though the mechanism by which the association of the pigments takes place is not completely understood at the present time.

In an attempt to determine the mechanism by which the organic pigments are maintained in close association with the carbon black, a series of tests were developed with various compositions as follows:

(1) An image was developed with an organosol type developer in which the pigment was an organic pigment;

(2) A second image of substantially the same configuration as (l) was developed with a second developer utilizing a carbon black pigment dispersed in a resin and in a carrier liquid; and

(3) An image was developed with a developer composition of the present invention wherein the marking particle consisted of the same organic pigment and the same carbon black pigment, both surrounded by an envelope of the same resin and present as a dispersed phase in a liquid carrier.

Photomicrographs of the resultant images indicated that the resolution and definition of the first and third prints were essentially equal while the definition and resolution of the second print showed some reduced image quality because of secondary pigment deposition around the image areas and non-uniform deposition in the image areas. From this series of tests, it was concluded in the case of prints 1 and 3 that the combination of pigment and resin of print 1 and the combination of carbon black, pigment and resin .of print 3 moved as a unit to the image areas as opposed to separate deposition on the image areas and areas immediately surrounding the image areas as was the case with print 2. If the carbon black, and solid surface active agent (organic pigment) and resin of the composition in accordance with the present invention had not moved as a unit, the developed print would have exhibited the secondary deposition noted in the photomicrograph of print 2 wherein carbon black was deposited in the areas immediately adjacent the image areas.

In a second series of tests to determine the physical characteristics of the deposited image prior to fixing, the procedure included charging, exposing and developing three separate images with each of the three developers noted above followed by a squeegee operation in which a roller was utilized to remove a substantial portion of the depleted developer or carrier liquid on the image bearing surface, and thereafter the images were air dried to efiect substantial permanent fixing of the marking element to the surface. Images developed with the developer compositions 1 and 3 after squeegeeing showed essentially the same definition and resolution as the first corresponding set of prints in which no squeegee operation was used. A print made from developer composition 2 followed by a squeegee operation showed that at least a portion of the image deposit was removed in comparison to the corresponding print of the earlier test using composition 2 wherein the image was not squeegeed. Further, the squeegeed print made from composition 2 showed a marked reduction in resolution and definition after the squeegee operation. Further, this series of tests indicated that the deposited image of developer compositions 1 and 3 was more resistant to mechanical smudging, rearrangement or deterioration during processing than the deposited image of composition 2.

For further details with respect to the developer composition of print 1 reference is made to application Ser. No. 362,961, filed of even date herewith.

In accordance with the present invention, the organic pigment is present in association with the carbon black in an amount sufiicient to provide the stabilization of coordinating medium for the carbon black and resin envelope. The carbon black pigment may thus be present as the remainder to provide the desired blackness and contrast as well as the covering power, which is characteristic of the carbon blacks. For the purposes of the 3,391,015 9 10 present invention, the organic pigment may be present becontent of said developer being between about .25% and tween about 1% and 80% by weight and the carbon black 3% by weight and the total pigment to resin ratio being may be present between about 99% and 20% by Weight between 122.5 and 1:70, said carbon black pigment and of total pigment. said solid organic pigment being characterized by a po- The following specific examples are illustrative of the 5 larity and electrophoretic mobility in said carrier which is compositions in accordance with the present invention: a function of the pH of each said pigment in an aqueous Example Surface Active Agent or Carbon Black Resin Polarity Carrier Comment Organic Pigment 1 2.3 grams of Phthaloeyanine- .7 gram of Neo Spectra 60 grams (70% solids) of Negative Odorless Min- Zulu Blue #4863. Mark 1110. an alkyd resin acid eral Thinner.

No. 8, Vise F-1+ 65% Soya, 24%.

Phthalie Auhydride. 2 1.5 grams of 4863 1.5 grams of Neo Spectra do .do "do Mark 1110. 3 .6 gram Benzidine Yellow .8 gram of Witcoblak F-3 d Positive do Toner 3D-2052, .9 gram Permanent Red-2B, Citation, Med. Yel. 1059, .8 gram Phthalocyanine-Zulu Blue, Flee. res. 4863. 4 .8 gram Permanent Red-2B, .6 gram of Superjet M-1011. 81 grams of resin supra ..do do Citation Lt. (Ba) 1058, .4 gram 3D-2052, 1.2 grams Phthalocyanine-Zulu Blue Toner 4852. 5 .8 gram 1058, .4 gram 3D- do .do "do do 2052, 1.2 grams 4852. 6 1.1 grams of 4852, .5 gram of .2 gram oi M-1011 81 grams of resin supra do do 266 grams of 3D-2052, 1.2 gram of 1058. (pigment resin ratio odorless 1:20). mineral thinner. 7 1.0 gram of 1058, 1.2 grams of .4 gram of M-101l 81 grams of resin supra ..do do Do.

4852, .4 gram of 3D-2052. 8 .8 gram of 1058, 1.2 grams of .6 gram of M-1011 ..do ..do do Do.

4852, .4 gram of 3D-2052. 9 1.0 gram of 1058, 1.3 grams of .2 gram of Witcoblak F3.. Resin supra to provide do do Do.

4852, .5 gram of 3D-2052. pigsnent resin ratio of 10 .8 gram of 1058, 1.0 gram of .8 gram of F-3 :do do .do Do.

4852, .4 gram of 3D-2052.

In general, by using organic pigments having a pH of medium, the polarity of said pigments being positive at a at least about 6.4, positive developers may be formulated pH above 6.4 and being negative at a pH below 6.4, the in accordance with the principles of the present invention, pH of said carbon black pigment and said solid organic while organic pigments of a pH of below about 6.4 propigment being relatively close to each other to provide vide negative developers. Since the pigmented portion of marking particles having essentially the same electrophothe marking particle is composed of carbon black and the retic mobility in said carrier, said method comprising the organic pigments, various hues and tints are possible 40 steps of contacting the surface of said image bearing memthrough appropriate choice of the organic pigment solid bers having an electrostatic latent image thereon with said surface active agent used in conjunction with the various liquid developer, said electrostatic charge causing migracarbon blacks previously mentioned. It is preferred that tron of said marking elements through said carrier at an the carbon black and the solid surface active agent be of electrophoretic mobility rate which is a function of the similar pH value. pH of each pigment and deposition thereof on said image While the present invention has been described with bearing surface, the deposition of said marking elements reference to electrophotography, it is to be understood on sald image bearing surface under the influence of said that the principles thereof are equally applicable to deelectrostatic latent image operative to increase the convelopers and methods of developing electrostatic images centratlon of resin in the area of deposition of said markon an electrically insulating surface which have been ing elements thereby decreasing the ratio of carrier to formed by other means well known in the art. Accordingresin below a ratio of 4:1, the increase in concentration ly, the present invention has been described with reference of he resin operative to form a continuous phase of resin to specific examples and methods, as well as preferred an carrier and an essentially continuous film of resin, embodiments thereof, and it is not intended that such and removing the carrier to effect adhesion of said resin details be regarded as limitations upon the scope of the to said image bearing surface to provide a substantially invention except so far as is included in the accompanypermanent developed image thereon. in claim:

What is claimed is: References Cited 1. The method of developing an electrostatic latent UNITED STATES PATENTS image on an image bearing member with a liquid developer wherein said developer includes marking elements fi z I ;i; X dispersed in an electrically insulating carrier liquid having 3058914 10/1962 i a K-B value of between 20 and 70, said marking elements 3076722 2/1963 e e a having a charge of the same polarity and comprising as 3O78231 2/1963 E";" the essential ingredients a carbon black pigment, a solid 65 308O251 3/1963 ea c e a surface active agent and a resin, said solid surface active 3084043 4/1963 g g 11 37 X agent being an organic pigment insoluble in said carrier 3102026 8/1963 i i i 'gi Z X liquid and present in an amount by weight of between 1% 3104169 9/1963 Metcalfe et X and 80% of the pigment weight, said resin forming an en- 3198649 8/1965 Metcalfe et a1 X velope around said pigment component to provide a two- 3:241:957 3/1966 Fauser et aL 117 37 X phase system of carrier and marking elements, said resin 3 244 633 4 19 Yenin et aL being an oil modified alkyd resin and characterized by the 3,257,322 19 wright X formation of an emulsion in said carrier when diluted to between 4 and 800 times the weight thereof with a carrier WILLIAM MARTIN Examinerliquid having a K-B value of between 20 and 70, the solids E. I. CABIC, Assistant Examiner. 

